The present invention relates to a serial printer having a single type wheel and adapted for use in a checkwriter or a numbering machine, which prints an amount of money or other information on a printing sheet fed gradually along a print line with respect to the type wheel.
Printers of this type are so-called serial printers. The serial printers are discriminated from printers of the so-called parallel type or simultaneous-lever type, in which a number of type wheels are arranged along an axis, corresponding to individual columns. An example of the parallel type is disclosed in U.S. Pat. No. 4,424,743. Although it does not require column-by-column feed of a printing sheet, this parallel printer must use so many type wheels that it cannot be easily reduced in cost, and is bulky as a whole. Also, the type wheels of this printer must be subjected to a substantial rotational load.
The serial printers, on the other hand, are conventionally incorporated in checkwriters of the so-called manual rotary type, in which a series of operations, including a printing operation, is performed by manually rotating a type wheel.
Although the printers of this type have the advantage of inexpensiveness, they are low in operating efficiency and cannot produce prints of very high quality.
Accordingly, there have been proposed serial printers which are arranged so that such a series of operations are performed by means of a power drive system, e.g., a motor drive system. One such printer is disclosed in Japanese Utility Model Disclosure No. 59-41556.
According to these proposed printers, however, the type selecting operation, printing operation using a hammering mechanism, and sheet feed operation are performed with use of different drive means, such as stepping motors. Therefore, the internal mechanisms and control systems are complicated, and the use of the stepping motors, which are considerably expensive, spoils the advantages of the serial printers, i.e., inexpensiveness and compactness.
Electric numbering machines having a single type wheel are disclosed in U.S. Pat. No. 4,406,551, Japanese Utility Model Disclosure No. 57-98852, and Japanese Utility Model Publication No. 60-2930. These machines, however, also use pulse motors and a number of solenoid devices as their power sources. Although only one type wheel is used in these machines, moreover, it is designed so as to slide along its axis of rotation during the printing operation. Inevitably, therefore, the machines are bulky, and are subject to the same drawbacks of the foregoing proposed printers.
In one such conventional serial printer, e.g., one used in a checkwriter, an amount of money is printed in the following manner. First, the type wheel is rotated selectively to situate a desired type in a printing position. Then, " " or other monetary unit mark is printed in a first column position, figures in the subsequent positions, and "*" or other indelible end mark in the last position.
During the process of these printing operations, the type wheel is repeatedly pressed against and separated from the printing sheet for each process. In order to prevent the sheet from being dislocated when the type wheel is disengaged therefrom, the printer of this type is provided with a sheet holding device. The holding device includes sheet holding rollers which are adapted to be pressed against the sheet during the printing operation, and to be disengaged from the sheet when the last end mark is printed.
An example of such a prior art sheet holding device is disclosed in Japanese Utility Model Publication No. 59-23015. In this sheet holding device, the sheet holding rollers are expected to be expressly set in a sheet holding position by a user's operation of a manual lever. When the end mark is printed, in this case, a release lever is operated to release the set rollers.
According to this arrangement, however, the sheet holding rollers must be set manually, thus requiring troublesome operation.
Alternative arrangements have been proposed in which the sheet holding rollers are disengaged from the sheet with the use of a separate power drive means. Disclosed in Japanese Patent Publication No. 57-55077, for example, is an arrangement such that the sheet holding rollers are disengaged by using a cam member having two cam surfaces, and the disengaging operation is controlled by means of an electromagnet. In an arrangement disclosed in Japanese Patent Publication No. 57-9949, moreover, a drive lever for sheet holding is set by means of a clutch-operated rotary cam, and is released or returned by means of a separated release cam. In either case, however, a drive mechanism for sheet holding must be provided independently of a printing drive system, thus making the printer more complicated and large-sized.
In gradually feeding the printing sheet along the print line to each printing position, in the serial printer of this type, a known mechanism is used for adjusted sheet feed, e.g., half-pitch feed, whose feed pitch is different from the regular feed pitch for the printing of figures and other regular characters. The half-pitch sheet feed is performed in printing a comma or other specific character, in order to prevent corruption and improve the appearance of the print.
As prior art examples, printers of the so-called manual rotary type are disclosed in Japanese Utility Model Publication Nos. 44-10342 and 48-7855. In these printers, a type wheel is set and depressed manually.
According to the arrangement of these printers, however, the printing process is followed by a resetting process in which the type wheel is rotated to be returned to its initial position. If a sheet feed process is tried simultaneously with the resetting process, therefore, the set state of the type carrying the comma or other specific character will be changed by the rotation of the type wheel. Thus, it is hard to adjust the sheet feed pitch in time with the set state.